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Synthesis of Alum
Second Quiz (Density/Alum
Collect lab-report (Density) and Pre-Lab (Alum)
Lecture on Today’s Experiment
Demostrate how to perform gravity filtration, suction filtration and Bunsen burner
Lecture:
Goal: synthesize alum from Aluminum can
- Learn to perform laboratory technique of purification by filtration
- Calculating theoretical yield and percent yield
Chemical formula for Alum : KAl(SO4)2 · 12H2O
Alum – use in medical, cooking, water treatment etc,…..
Chemical RXN – Handout
2Al(s) + 2KOH(aq) + 6H2O(l)  2K[Al(OH)4] + 3H2(g)
 step 3-4 : Dissolve metal in excess strong base KOH to form a complex ion and H2 gas (bubbles)
 use gravity filtration to filter the solution while it’s still hot, keep the filtrate (What is the filtrate)
2K[Al(OH)4](aq) + H2SO4 (l)  2Al(OH)3(s) + 2H2O(l) + K2SO4(aq)
 step 8: Neutralize excess –OH in the filtrate with H2SO4  precipitation will form
2Al(OH)3(s) + 3H2SO4(aq) + K2SO4  2KAl(SO4)2 (aq) + 6H2O(l)
 Step 9: more acid is added to dissolve Al(OH)3 solid to form a soluble KAl(SO4)2, this is not really an
Hydrated Alum
KAl(SO4)2(aq) + excess H2O (0oC)  KAl(SO4)2 · 12H2O
 this can be filter using suction filtration and dry
 Student must wait after 48 hours to weigh their sample and must be done prior the next class meeting
(penalty will be applied)
 Prefer to the class schedule to check when the lab will open, you should come 1 hour after the lab
start and must ask for permission (WEAR GOGGLES!!!!)
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Theoretical Yield: maximum amount of product possible base on the amount o reactant
Calculation:
gAl  moles Al  moles Alum  g Alum
Percent Yield =
Filtration:
Things to do for next week
1.
Quiz # 3 (Alum/Analysis of a hydrated metal Sulfate_week 1)
2.
Turn in Report for Alum
3.
Pre-lab ( Hydrated Metal Sulfate_week 1)
4.
Collect 4’’ test tube per pair for unknown
5.
Get Instructor’s signature
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